1. Field of the Invention
This invention generally relates to pumping systems. More specifically this invention relates to pumping systems for removing a first liquid, such as spilled hydrocarbons, from the surface of a second liquid, such as ground water.
2. Description of Related Art
When hydrocarbons or similar polluting substances spill, they can seep into the ground. Such pollutants have a lower specific gravity than water and generally are immiscible in water. Consequently, they accumulate or float on the surface of the ground water as they permeate the ground and contaminate the surrounding aquifer. Existing recovery apparatus uses different techniques for recovering such pollutants from ground water. Generally these techniques rely on different physical and chemical properties of the ground water and pollutants.
One such technique, called "skimming", relies on the different specific gravities of the ground water and pollutants and the immiscibility of the two liquids.
The skimming process generally includes the drilling of one or more wells. Each well provides access to the ground water and pollutants that accumulate in the well to facilitate the removal of the pollutants. The removed pollutant may be processed on site or stored in containers for removal to an authorized disposal site. It is important that the cleanup apparatus discriminate the pollutant and noncontaminated ground water to minimize the storage or processing requirements of materials recovered as pollutants.
The cleanup process may also include ground water processing particularly as a condition precedent to returning ground water to the aquifer. As such processing may include aerating or filtering steps, it also is important that the apparatus discriminate ground water from pollutants to assure that materials processed as ground water are essentially pollutant free.
The following patents disclose two embodiments of recovery apparatus used in such skimming procedures:
______________________________________ 4,497,370 (1985) Breslin 4,663,037 (1987) Breslin ______________________________________
The Breslin (370) patent discloses recovery apparatus that utilizes a hollow housing covered by a semi-permeable membrane. The membrane passes liquid hydrocarbons, but blocks the flow of ground water into the housing. The liquid hydrocarbons then can be moved to a receptacle by suction applied to the housing, by pressurization of the well casing or using submersible pumps.
In accordance with the Breslin (037) patent a recovery unit lowered into a well sinks in the hydrocarbons, but floats in the ground water. A remote pumping facility sucks the hydrocarbons out of the well through an inlet port located in the hydrocarbon layer.
Both of these approaches can be effective for significant layers of hydrocarbons. However each relies on the natural migration of the hydrocarbons to the well site, so once the pumping system extracts the hydrocarbons around the well, a significant time may result before additional hydrocarbons migrate to the well site. Moreover, as the hydrocarbon layer becomes thin, it becomes difficult for the recovery system to discriminate hydrocarbons and ground water.
Other recovery apparatus decreases recovery time by locating a pump in a well to form a cone of depression, as described in the following patents:
______________________________________ 4,273,650 (1981) Solomon 4,527,633 (1985) McLaughlin et al 4,546,830 (1985) McLaughlin et al 4,625,807 (1986) Harlow 4,826,406 (1989) Wells 4,934,458 (1990) Warburton et al ______________________________________
In each of these references pumping apparatus extracts ground water from the well thereby lowering the ground water level in and proximate the well. Lowering the ground water level accelerates the influx of the pollutant and facilitates the skimming operation. Characteristically recovery apparatus that produces a cone of depression uses one pumping structure for pumping the ground water and another, independent pumping structure for removing the pollutants.
In the Solomon patent, for example, a pump in the bottom of a well ejects ground water from the well to form the cone of depression. A second pumping system periodically pumps the material that accumulates in the cone of depression to a recovery tank or similar structure.
The McLaughlin et al patents utilize independent compressed air pumping systems for forming the cone of depression and for removing the pollutants respectively. Compressed air pumping systems avoid the potential for fire that could occur if electrical motors are located in or proximate hydrocarbons.
The Harlow patent discloses a pump for forming a cone of depression. Compressed air from an external source moves the pollutant by driving a piston pump.
The Wells patent discloses a submersible system with an open top sleeve that extends above the pump system for skimming the upper portion of any liquid collected in a cone of depression. An independent compressed air pump forces skimmed materials to a recovery system.
The Warburton patent also discloses a system for producing a cone of depression with separate electrical pumping systems submerged in the ground water. A long hose extends from the pollutant pump to the cone. It is necessary to adjust the entrance of the hose to lie in the accumulated hydrocarbons.
Other pumping systems that pump one liquid separately from another liquid often include separate variable volume chambers as shown in the following references:
______________________________________ 1,797,533 (1931) Stokes 3,218,979 (1965) Baldwin 3,692,433 (1972) Finger 4,389,737 (1983) Robinson et al 2,184,791 (1987) Hoya (Great Britain) 4,975,027 (1990) Halverson et al ______________________________________
The Stokes patent discloses an expansible chamber utilized in conjunction with a flash steam generator for pumping water. The Baldwin and Robinson patents disclose blood pumps in which one liquid, such as a hydraulic liquid or saline solution, changes a pumping volume to displace blood. The Finger patent discloses a piston pump with input and output conduits. A parallel system damps pressure variations induced by piston action. In accordance with the Hoya patent, a pump for displacing a slurry, as one liquid, operates in response to hydraulic fluid, as a second liquid, acting on a reciprocating piston to change the volume of a slurry pumping chamber. The Halverson et al patent discloses a transfer pump with a piston and a bellows. The pump is adapted for use in vacuum applications.
Other patents that disclose apparatus with variable volume pumping chambers for lifting liquids from deep wells, include:
______________________________________ 2,810,353 (1957) Bower 3,253,549 (1966) Vincent et al 4,008,008 (1977) Vergnet 4,222,440 (1980) Parker 4,580,952 (1986) Eberle WO 87/05974 (1987) Dickinson et al ______________________________________
The Bower patent discloses a flexible bladder for pumping liquid from a well. A torsion rod twists to contract the bladder and pump any contents therefrom. Releasing the torsion rod allows the bladder to fill with oil.
In the Vincent et al patent, a power fluid operates on a reciprocating plunger acting through a pipe on a liquid to expand and contract a bladder alternately thereby to pump another liquid from a well to a surface.
The Vergnet patent discloses a reciprocating piston that acts through a long tube to contract and expand a bladder. The bladder is located in a fixed housing with inlet and outlet valve structures and pumps liquid into and out of the housing thereby to force a liquid from a well.
In the Parker patent pumping apparatus includes inverted inner and outer cups. The outer cup connects to atmosphere via capillary tube while the inner cup is a closed dome. Liquid passes through a check valve in the bottom of the outer cup to rise in the closed dome. When the capillary is pressurized from above a well, the check valve closes and the pressure in the outer cup causes liquid to rise in the dome and compress the air trapped in the dome. When the capillary is suddenly opened to atmospheric pressure, the entrapped compressed air drives the fluid in the first cup through the capillary.
In the Eberle patent a hydraulic pump alternately expands and contracts a bladder in a chamber with inlet and outlet valve structures.
In the Dickinson et al patent a bladder pump, suspended in a tubular airlift pump housing, responds to pressure variations of compressed air to expand and contract the bladder.
Variable volume pumping systems using bladder-type pumps like those described above have not been used in recovery systems for skimming pollutants from ground water. First, prior art bladder-type pumps have not produced flow rates that are sufficient to form a cone of depression in many applications. Thus, the need for a high flow rate ground water pumping systems remains. The use of these pumping systems as pollutant pumps might seem appropriate. However, these prior art bladder systems require additional structures for expanding and contracting a bladder. The resulting increase in apparatus and operating costs and complexity and potential decrease in apparatus reliably over the existing two-pump recovery apparatus is not justified.
Cone of depression recovery apparatus with independent pumping systems have certain characteristic limitations. For example, the requirement for a second pumping system increases the overall manufacturing costs of the recovery apparatus. Such apparatus also requires complex control systems to assure that the materials pumped by each pumping system are product and ground water, respectively. If a risk of fire and explosion in the event of an electrical fault is of paramount concern, pneumatic pumping systems are selected with their attendant air compressors. However, air compressor motors must be much larger than electrically-operated pump motors for equal performance. Moreover, pneumatically-operated pumps require filters, driers and other apparatus to provide a clean, dry source of air. Thus, pneumatic systems are costly, electrically inefficient and difficult to maintain. Nevertheless, existing cone of depression recovery apparatus continues to utilize both electrically and pneumatically independent dual pumping systems for pumping ground water and recovered pollutants.